A vehicle occupant restraint system having an inflatable air bag is known. Typically, an inflatable air bag is inflated by gas directed into the air bag in response to the vehicle experiencing deceleration indicative of a collision. The inflated air bag absorbs energy resulting from the forward movement of an occupant against the air bag. The energy absorbed by the air bag is dissipated to minimize rebounding of the occupant from the air bag.
One way to dissipate the energy absorbed by the air bag is to vent the gas in the air bag. It is known to vent the gas in the air bag through a vent hole to the atmosphere. The vent hole may be covered with a patch which opens when a predetermined pressure level is reached inside the air bag. When the patch opens, gas inside the air bag passes through the vent hole to the atmosphere.